The invention relates to a power demand control method of switching loads by prediction in a plant facility supplied by energy from a utility company in order to keep the demand at the end of a period of control within a demand limit assigned at the beginning of the period.
The prior art of power demand control has been described and the technique used has been disclosed in U.S. Pat. No. 3,872,286 of Putman, issued on Mar. 18, 1975. For the purpose of the description hereinafter of the present invention, the description and drawings of the Putman patent are hereby incorporated by reference. The prior art has shown that it is desirable to switch loads as early as possible in the demand period in order to have a maximum degree of freedom for control with the available loads, while being able to meet the target at the end of the period. For instance, in the Putman patent, during the first minutes of the period, the control system is allowed not to de-energize any load, thus letting the installation and equipment of the plant follow its needs without any constraint from the controller. This is a way of maximizing the use of the available energy, without forgoing the possibility of a heavy control later in the period in order to still meet the demand limit. This method, however, being the all or nothing approach, may run the risk that effective control at a later time is no longer possible. Moreover, the loads liberated in the first period because of the absence of control might not be the most judicious ones.
In contrast, the present invention proposes to maximize the utilization of the energy within the assigned demand limit without giving up control at any time during the period.
An object of the present invention is to control the loads in a plant facility in order to maximize the use of the loads within an assigned demand limit.
Another object of the present invention is to control the loads during a period of control by prediction of a final demand at the edn of the period, an instantaneous demand being controllably achieved at selected operative points during the period.
A further object of the present invention is to integrate the consumption of energy by selective switching of the loads in a plant facility along a predetermined integration curve intersecting a desired target at the end of the period.
Still another object of the present invention is to meet at the end of a period of control limit assigned to the demand of energy called by the loads in a plant facility through successive approximations performed along a monotonic curve as a result of control of the loads during the demand period. Achieving such maximization by the control method according to the invention stems from a maximum permissible limit achieved at each operative point during the demand period with the maximum permissible limit being varied as a function of time during control.
Therefore, a further object of the present invention is to maximize (by power demand control) the amount of energy consumed during a period of control of the loads in a plant facility while staying within a demand limit assigned at the beginning of the demand period, the control method imposing a limiting control condition at each operative point during the demand period.